This invention relates to a system and process for sorting pieces of materials (by composition) in a stream of materials moving along a conveyor belt. Particularly, this invention relates to a system and process for classifying pieces of materials of unknown composition based on the x-ray fluorescence spectrum of each respective piece so as to permit very high speed sorting of the unknown materials.
Current worldwide environmental concerns have fueled an increase in efforts to recycle used equipment and articles containing materials that can be reused. Such efforts have produced new and improved processes for sorting materials such as plastics, glass, metals, and metal alloys.
As used herein, a xe2x80x9cmaterialxe2x80x9d may be a chemical element, a compound or mixture of chemical elements, or a compound or mixture of a compound or mixture of chemical elements, wherein the complexity of a compound or mixture may range from being simple to complex. Materials may include metals (ferrous and non-ferrous), metal alloys, plastics, rubber, glass, ceramics, etc. As used herein, element means a chemical element of the periodic table of elements, including elements that may be discovered after the filing date of this application.
Generally, methods for sorting pieces of materials involve determining a physical property or properties of each piece, and grouping together pieces sharing a common property or properties. Such properties may include color, hue, texture, weight, density, transmissivity to light, sound, or other signals, and reaction to stimuli such as various fields. Methods to determine these properties include visual identification of a material by a person, identification by the amount and/or wavelength of the light waves emitted or transmitted, eddy-current separation, heavy-media plant separation, and x-ray fluorescence detection.
With respect to metals and metal alloys, today it is neither technically nor commercially feasible to separate and recover many of the non-ferrous metals that are manufactured into products and discarded at the end of their useful life. In residential waste, only aluminum cans are recycled to any significant degree. Virtually none of the other non-ferrous materials in our residential waste are recovered. Instead, they are disposed in landfills. Further, small non-ferrous materials below ⅝ inches in size are landfilled from nearly 200 automobile shredders.
Smaller-sized pieces of non-ferrous metals from automobile shredders are not separated because their recovery is not cost-effective. They can only be consolidated and shipped to larger facilities for further processing. Mixed non-ferrous metals from industrial processes are often disposed or junked because hand-sorting and small-particle recovery technologies either do not work well or are not cost-effective. Nearly 2 billion pounds of valuable non-ferrous metals are discarded in landfills every year in the U.S. alone. Worldwide, the amount of metal wasted is far greater. If this metal could be economically recycled at high volumes, the potential value generated is estimated to be in excess of 1 billion dollars (U.S.) per year. Further, there are approximately 200 waste-to-energy facilities, 200 automobile shredders, and thousands of metal scrap yards in the U.S. alone that could benefit financially (and otherwise) from an improved sorting system.
X-ray fluorescence spectroscopy has long been a useful analytical tool in the laboratory for classifying materials by identifying elements within the material, both in academic environments and in industry. The use of characteristic x-rays such as, for example, K-shell or L-shell x-rays, emitted under excitation provides a method for positive identification of elements and their relative amounts present in different materials, such as metals and metal alloys. For example, radiation striking matter causes the emission of characteristic K-shell x-rays when a K-shell electron is knocked out of the K-shell by incoming radiation and is then replaced by an outer shell electron. The outer electron, in dropping to the K-shell energy state, emits x-ray radiation characteristics of the atom.
The energy of emitted x-rays depends on the atomic number of the fluorescing elements. Energy-resolving detectors can detect the different energy levels at which x-rays are fluoresced, and generate an x-ray signal from the detected x-rays. This x-ray signal may then be used to build an energy spectrum of the detected x-rays, and from the information, the element or elements which produced the x-rays may be identified. Fluorescent x-rays are emitted isotopically from an irradiated element and the detected radiation depends on the solid angle subtended by the detector and any absorption of this radiation prior to the radiation reaching the detector. The lower the energy of an x-ray, the shorter the distance it will travel before being absorbed by air. Thus, when detecting x-rays, the amount of x-rays detected is a function of the quantity of x-rays emitted, the energy level of the emitted x-rays, the emitted x-rays absorbed in the transmission medium, the angles between the detected x-rays and the detector, and the distance between the detector and the irradiated material.
Although x-ray spectroscopy is a useful analytical tool for classifying materials, with current technology, the cost is high per analysis, and the time required is typically minutes or hours. Scrap yard identification of metals and alloys is primarily accomplished today by trained sorters who visually examine each metal object one at a time. Contamination is removed by shearing. A trained sorter observes subtle characteristics of color, hue, texture, and density to qualitatively assess the composition of the metal. Sometimes, spark testing or chemical xe2x80x9clitmusxe2x80x9d testing aids in identification. The process is slow and inaccurate, but is the most common method in existence today for sorting scrap metal to upgrade its value.
There have been disclosed a variety of systems and techniques for classifying materials based on the x-ray fluorescence of the material. Some of these systems involve hand-held or bench-top x-ray fluorescence detectors. Some of these systems include serially conveying pieces of material along a conveyor belt and irradiating each piece, in turn, with x-rays. These x-rays cause each piece of material to fluoresce x-rays at various energy levels, depending on the elements contained in the piece. The fluoresced x-rays are detected, and the piece of material is then classified based on the fluoresced x-rays and sorted in accordance with this classification.
Such disclosed systems, however, have not been widely accepted commercially because they require about one second or more to detect the x-rays and accurately classify the piece of material accordingly, and they are expensive relative to the number of objects identified per unit time.
In response to the need for faster classification, disclosed herein is a system and process for classifying a piece of material based on the x-ray fluorescence of its constituents, wherein x-rays are detected from the piece and the piece is accurately classified, cumulatively, in substantially less than a secondxe2x80x94indeed, typically in about 100 milliseconds (ms) or less.
To achieve these speeds, a high intensity x-ray source, such as an x-ray tube, is used to irradiate the piece. The previously mentioned systems, by contrast, employ a comparatively low-power narrow-spectrum x-ray source such as, for example, Cadmium isotope Cd129, Americium isotope Am241, Cobalt isotope Co57, and Iron isotope Fe55. Although use of an x-ray tube has been mentioned as a possible alternative x-ray source for a material sorting system, a high intensity x-ray source has not been implemented by others in such systems, and there are major problems in doing so that have not previously been resolved. Consequently, there previously has not been shown a system that enables use of a high intensity x-ray source in such a system.
Another problem with many known material sorting systems that classify pieces of material based on the x-ray fluorescence of the material is that such systems are limited to analyzing only the fluorescence of specific, predetermined elements of interest in the piece of material. Analyzing only select fluorescence limits the accuracy of the identification and the range of materials that can be identified.
In response to this problem, there is also disclosed herein a system and process for classifying a piece of material based on the x-ray fluorescence of the piece by recognizing a broad spectral pattern of the x-ray fluorescence.
According to the invention, a high speed process for classifying a piece of material of unknown composition is provided. The piece is irradiated with x-rays from an x-ray source, causing the piece to fluoresce x-rays. The fluoresced x-rays are detected with an x-ray detector and the piece is classified from the detected fluoresced x-rays.
In optional illustrative embodiments, detecting and classifying are cumulatively performed in less than one second, less than 500 ms, less than 100 ms, less than 50 ms, and preferably even less than 15 ms.
Preferably, but optionally, an x-ray fluorescence spectrum of the piece of material from the detected fluoresced x-rays is determined, and at least one of the steps of the irradiating and detecting includes conditioning the irradiating x-rays or the fluoresced x-rays, respectively, such that speed and accuracy of determining the x-ray fluorescence spectrum is not significantly compromised or complicated by generation or detection of extraneous x-rays.
In yet another optional aspect, the irradiating x-rays are filtered to reduce a number of irradiating x-rays having an energy level too low to cause the piece to fluoresce x-rays having an energy level within a predefined range of the x-ray fluorescence spectrum.
In still another optional aspect, the irradiating x-rays are aimed at the piece of material to reduce an amount of x-rays detected by the x-ray detector that were not fluoresced by the piece itself.
In still another optional aspect of the illustrated embodiments, the x-ray fluorescence spectrum is determined for a predefined range of energy levels, and the irradiating x-rays are aimed by collimating the x-ray source with a collimator whose aperture components are made substantially of one or more materials that fluoresce at energy levels not within the predefined range.
For example, the operative parts of the collimator may be formed essentially of polyvinyl chloride.
In another optional aspect, the x-ray source is aimed at the piece of material with a small aperture to substantially confine the x-rays detected by the x-ray detector to those fluoresced by the piece and limit detection of other x-rays.
In another optional aspect, the x-ray detection is aimed by collimating the x-ray detector with a collimator consisting essentially of one or more materials that fluoresce at energy levels not within the predefined range. For example, the collimator may be formed essentially of polyvinyl chloride.
In yet another optional aspect, the piece of material is conveyed on a conveyor through a detection area where the irradiating x-rays irradiate the piece and the fluoresced x-rays are detected from the piece. The conveyor may be formed essentially of one or more materials that fluoresce at energy levels not within the predefined energy range, so that the conveyor does not fluoresce x-rays that significantly interfere with determination of the x-ray fluorescence spectrum of the piece.
In another optional aspect, the spectral pattern of the determined x-ray fluorescence spectrum is recognized.
In still another optional aspect, a plurality of x-ray fluorescence spectra are stored as reference spectra on a computer-readable medium, each reference spectrum having a spectral pattern and corresponding to a different material classification. Recognizing the detected spectral pattern includes comparing the determined x-ray fluorescence spectrum to each of the reference spectra to determine which reference spectrum has a spectral pattern most similar to the spectral pattern of the determined x-ray fluorescence spectrum. The piece of material is classified as the material classification corresponding to the reference spectrum determined to have the most similar spectral pattern.
In a further optional aspect, the piece of material is conveyed on a conveyor and through a detection area where the irradiating x-rays irradiate the piece and the fluoresced x-rays are detected from the piece, and an ejector corresponding to the classification of the piece is actuated such that the piece is ejected from the conveyor at a point downstream from the detection area and associated with said classification.
In another optional aspect, the piece of material is flattened prior to irradiation and detection.
In still another optional aspect, the step of irradiating includes irradiating the x-rays at a high intensity.
Optionally, but preferably, the x-ray source is an x-ray tube.
It will be appreciated that both large and small pieces may be processed, including pieces having a largest dimension less than ⅝ inch; indeed, even less than approximately xc2xc inch.
In another illustrative embodiment, a system for classifying a piece of material of unknown composition is provided, where the system is connected to a power supply. An x-ray source powered by the power supply generates x-rays that irradiate the piece of material, causing the piece to fluoresce x-rays. An x-ray detector detects the fluoresced x-rays and produces as an output a signal, called an x-ray signal, representing the detected x-rays. An x-ray fluorescence processing module is connected to the x-ray detector. The processing module receives as an input the x-ray signal and generates as an output a classification signal that identifies the classification of the piece of material.
In optional aspects, the x-ray detector and x-ray fluorescence processing module are operative to detect the fluoresced x-rays and classify the piece, respectively, in a combined time less than one second, less than 500 ms, less than 100 ms, less than 50 ms, and preferably even less than 15 ms.
In yet another optional aspect, the x-ray fluorescence processing module includes a spectrum acquisition module connected to the x-ray detector, the spectrum acquisition module receives as an input the x-ray signal and generates as an output an x-ray fluorescence spectrum, and a classification module receives as an input the x-ray fluorescence spectrum and generates as an output a classification signal indicating a classification of the piece of material. The system is conditioned such that accurate determination of the x-ray fluorescence spectrum is not significantly compromised or complicated by generation or detection of extraneous x-rays.
In another optional aspect of this embodiment, the x-ray fluorescence spectrum is determined for a predefined range of energy levels, and an x-ray filter filters the irradiating x-rays to reduce a number of irradiating x-rays having an energy level too low to cause the piece to fluoresce x-rays having an energy level within the predefined range of the x-ray fluorescence spectrum.
In another optional aspect the output of the x-ray source is conditioned by a collimator, the collimator having an aperture to aim the irradiating x-rays at the piece such that production of x-rays from objects other than the piece is reduced.
In an optional feature of this aspect, the x-ray fluorescence spectrum is determined for a predefined range of energy levels, aperture components of the collimator being made substantially of one or more materials that fluoresce at energy levels not within the predefined range.
For example, the collimator may be formed essentially of polyvinyl chloride.
In another optional aspect, the x-rays detected by the x-ray detector are conditioned by a collimator, the collimator having an aperture to aim the detection of the fluoresced x-rays at the piece during the detection such that detection of incident radiation from objects other than the piece is minimized.
For example, the collimator may be formed essentially of polyvinyl chloride.
In still another optional aspect, the x-ray fluorescence spectrum is determined for a predefined range of energy levels, and a conveyor conveys the piece of material through a detection area where the irradiating x-rays irradiate the piece and the fluoresced x-rays are detected from the piece, and the conveyor consists essentially of one or more materials that fluoresce at energy levels not within the predefined range.
For example, the conveyor belt may be formed essentially of polyvinyl chloride.
In another optional aspect, the x-ray fluorescence processing module includes a spectrum acquisition module connected to the x-ray detector, the spectrum acquisition module to receive as an input the x-ray signal and to generate as an output an x-ray fluorescence spectrum, and a classification module to receive as an input the x-ray fluorescence spectrum and to generate as an output a classification signal that indicates the classification of the piece, wherein the classification module is operative to classify the piece by recognizing a spectral pattern of the x-ray fluorescence spectrum.
In yet another optional aspect, a computer-readable storage medium stores a plurality of x-ray fluorescence spectra as reference spectra, each reference spectrum having a spectral pattern and corresponding to a different material classification, and the classification module further includes means for comparing the determined x-ray fluorescence spectrum to each of the reference spectra to determine which reference spectrum has a spectral pattern most similar to the spectral pattern of the determined x-ray fluorescence spectrum. The classification of the piece corresponds to the reference spectrum determined to have the most similar spectral pattern.
In a further optional aspect, a conveyor conveys the piece of material through a detection area where the irradiating x-rays irradiate the piece and the fluoresced x-rays are detected from the piece, and an ejector corresponding to the classification of the piece having an input receives an ejection signal, and the ejector ejects the piece from the conveyor in accordance with the ejection signal at a point downstream from the detection area and associated with said classification.
In another optional aspect, the piece of material is flattened prior to irradiation and detection.
In still another optional aspect, the x-ray source is operative to generate the irradiating x-rays at a high intensity.
Optionally, but preferably, the x-ray source is an x-ray tube.
In another illustrative embodiment, a system for classifying a piece of material of unknown composition at high speeds is provided. The system includes means for irradiating the piece with x-rays from an x-ray source, causing the piece to fluoresce x-rays, means for detecting the fluoresced x-rays with an x-ray detector, and means for classifying the piece of material from the detected fluoresced x-rays.
In optional illustrative embodiments, the means for detecting and means for classifying are operative to detect the fluoresced x-rays and classify the piece, respectively, in a combined time of less than one second, less than 500 ms, less than 100 ms, less than 50 ms, and preferably even less than 15 ms.
Preferably, but optionally, the system includes means for determining an x-ray fluorescence spectrum of the piece of material from the detected fluoresced x-rays, and means for conditioning at least one of the irradiating x-rays and the fluoresced x-rays, respectively, such that speed and accuracy of determining the x-ray fluorescence spectrum is not significantly compromised or complicated by generation and detection of extraneous x-rays.
In yet another optional aspect, the means for conditioning includes means for filtering the irradiating x-rays to reduce a number of irradiating x-rays having an energy level too low to cause the piece to fluoresce x-rays having an energy level within a predefined range of the x-ray fluorescence spectrum.
In another optional aspect of the illustrated embodiments, the means for conditioning includes means for aiming the irradiating x-rays at the piece of material to reduce an amount of x-rays detected by the x-ray detector that were not fluoresced by the piece itself.
Preferably, but optionally, the means for aiming includes a collimator whose aperture components are made substantially of one or more materials that fluoresce at energy levels not within the predefined range.
For example, operative parts of the collimator may be formed essentially of polyvinyl chloride.
In another optional aspect, the means for conditioning includes means for aiming the x-ray detector at the piece of material to substantially confine the x-rays detected by the x-ray detector to those fluoresced by the piece and limit detection of other x-rays.
In another optional aspect, the x-ray fluorescence spectrum is determined for a predefined range of energy levels, and the means for aiming the x-ray detector includes a collimator whose aperture components are made of one or more materials that fluoresce at energy levels not within the predefined range.
For example, operative parts of the collimator may be formed essentially of polyvinyl chloride.
In yet another optional aspect, the system further includes means for conveying the piece of material through a detection area where the irradiating x-rays irradiate the piece and the fluoresced x-rays are detected from the piece, and the means for conveying includes a conveyor that may be formed essentially of one or more materials that fluoresce at energy levels not within the predefined energy range of the determined x-ray fluorescence spectrum so that the conveyor does not fluoresce x-rays that significantly interfere with determination of the x-ray fluorescence spectrum of the piece.
In an optional aspect, the conveyor is made essentially of polyvinyl chloride.
In still another optional aspect, the system further includes means for recognizing the spectral pattern of the determined x-ray fluorescence spectrum, and the means for classifying the piece base the classification on the recognition of the spectral pattern.
In another optional aspect, the means for detecting, means for determining, means for recognizing, and means for classifying are operative to detect the fluoresced x-rays, determine the x-ray fluorescence spectrum, recognize the spectral pattern of the x-ray fluorescence spectrum, and classify the piece, respectively, in a combined time of less than one second.
In a further optional aspect, the system further includes means for storing a plurality of x-ray fluorescence spectra as reference spectra on a computer-readable medium, each reference spectrum having a spectral pattern and corresponding to a different material classification, and the means for recognizing the detected spectral pattern includes means for comparing the determined x-ray fluorescence spectrum to each of the reference spectra to determine which reference spectrum has a spectral pattern most similar to the spectral pattern of the determined x-ray fluorescence spectrum, and the piece of material is classified as the material classification corresponding to the reference spectrum determined to have the most similar spectral pattern.
In yet another optional aspect, the system further includes means for flattening the piece of material prior to irradiation and detection.
In still another optional aspect, the system further includes means for irradiating the x-rays at a high intensity.
Optionally, but preferably, the x-ray source is an x-ray tube.
In another optional aspect, the system further includes means for conveying the piece of material through a detection area where the irradiating x-rays irradiate the piece and the fluoresced x-rays are detected from the piece, and means for actuating an ejector corresponding to the classification of the piece such that the piece is ejected from the conveying means at a point downstream from the detection area and associated with said clarification.